The present invention relates generally to novel electrically conductive polymer compositions, to a process for producing these novel compositions, to substrates coated with a film formed from these novel compositions, and to oxidizing solutions for the production of these compositions.
Electrically conductive polymers and copolymers have proven in recent years to be materials which are particularly advantageous, on the one hand, in the field of microelectronics, especially in photolithographic processes, for example in order to improve electric charge flow, and on the other hand in electrochemistry, for example for the manufacture of rechargeable generators.
More specifically, in microelectronics, such materials are particularly useful for the manufacture of photosensitive conductive resins for processing by electron beam or deep ultraviolet, the manufacture of phase shift masks and conductive charge flow layers for examination by scanning electron microscope, or else plasma engraving. In electrochemistry, these materials are particularly suitable for the storage of electrochemical energy, the manufacture of antistatic conductive materials, and the applications of electrochromism.
Inherently conductive polymers and copolymers are known compounds, and among these polymers and copolymers there may be mentioned poly(thiophenes), polypyrroles, polyacetylenes, polyphenylenes, polythiophene-polypyrrole copolymers, and water-soluble derivatives thereof.
These inherently conductive polymers are generally doped with strong oxidizing compounds.
The compounds which are generally used for doping inherently conductive polymers and copolymers are arsenic pentafluoride (AsF.sub.5), ferric chloride (FeCl.sub.3), nitrosyl tetrafluoroborate (NOBF.sub.4), nitrosyl hexafluorophosphate (NOPF.sub.6), auric chloride (AuCl.sub.3) and ferric tosylate (Fe(OTs).sub.3).
These oxidizing compounds, when used to obtain electrically conductive-polymer compositions, have the disadvantage of comprising metal atoms, a fact which renders their use incompatible with the application of the conductive polymer compositions as photosensitive resins in photolithographic processes. In fact, the presence of metal ions such as boron, phosphorus, iron, arsenic, antimony and gold, for example, threatens to contaminate the various constituents of circuits manufactured from photosensitive resins, including conductive polymers doped with these oxidizing compounds, and therefore to interfere with their electronic properties.
Moreover, the majority of the conductive polymer compositions doped with the above oxidizing compounds show little resistance to aging; in other words, the conductivity of conductive films produced from such conductive polymer compositions decreases rapidly over time. This phenomenon is intensified under the effect of temperature and humidity.
The article titled "Stability studies of the electrical conductivity of various poly(3-alkylthiophenes)" by Y. Wang and M. F. Rubner in Synthetic Metals 39 (1990), pages 153-175, examines more particularly the thermal stability of various poly(3-alkylthiophenes) doped with FeCl.sub.3, Fe(OTs).sub.3 and NOPF.sub.6. This article mentions that the best thermal stability is obtained by using FeCl.sub.3 as oxidizing compound for doping polymers. Moreover, this article mentions that tests aimed at introducing the tosylate anion electrochemically, by using a purely organic compound, namely Bu.sub.4 NOTs, proved fruitless.
The article titled "Photoimaging of Electronically Polymeric Networks" by M. S. A Abdou, G. A. Diaz-Guijada, M. J. Arroyo and S. Holdcroft in Chem. Mater 1991, 3, pages 1003-1006, describes the doping of poly(3-hexylthiophene) with a solution of nitrosyl tetrafluoroborate in acetonitrile. This article also mentions that the polymer thus doped undergoes a marked loss in its conductivity after 30 minutes of atmospheric exposure.
The article "Conducting polymers as Deep-UV electron-beam resist: Direct production of Micrometer Scale conducting Structures from poly(3-octylthiophene)" by S. X. Cai, J. F. W. Keana, J. C. Nabity and M. N. Wybourne, Journal of Molecular Electronics, Vol 7, 1991, pages 63-68 describes the crosslinking of poly(3-octylthiophene) doped with FeCl.sub.3 with the aid of ethylenebis (4-azido-2,3,5,6-tetrafluorobenzoate) under the action of deep UV radiation. This polymer can be used as a negative resist in deep UV. It can be used for direct production of conductive structures on the micrometer scale by using electron beam lithography.
The article titled "Laser, direct-write microlithography of soluble thiophenes" by M. S. A. Abdou, Z. W. Xie, A. M. Leung and S. Holdcroft, Synthetic Metals, 52 (1992) pages 159-170 describes the production of polymer "wires" by a conventional semiconductor photolithography process using, for the production of the "wires", a film of poly(3-hexylthiophene) which is irradiated through a mask by ultraviolet or visible light. The nonirradiated areas of the film are removed by dissolution in an organic solvent, and the remaining polymer is subsequently oxidized with nitrosyl tetrafluoroborate or ferric chloride in order to obtain an electronically conductive pattern.
The article titled "Microlithography using conducting polymers" by J. Bargon, T. Weidenbruck and T. Ueno, SPIE Vol 1262, (1990) pages 565-568 describes lithographically structured, electrically conductive polymers which comprise polythiophenes and polypyrrole derivatives doped with FeCl.sub.3, Fe(ClO.sub.4).sub.3, Fe(NO.sub.3).sub.3, NH.sub.4 Ce(NO.sub.3).sub.5, FeBR.sub.3 sic! and peroxides.
Finally, the article titled "Oxidation of .pi.-conjugated polymers with gold trichloride: enhanced stability of the electronically conducting state and electroless deposition of Au.sup.0* " by M. S. A. Abdou and S. Holdcroft, Synthetic Metals, 60 (1993) pages 93-96, describes the oxidizing doping of poly(3-hexylthiophene) by means of a solution of AuCl.sub.3 in acetonitrile or nitromethane. The conductive polymers obtained are of high stability, especially in comparison with polymers doped with FeCl.sub.3.
Patent Application CA-2 070 043 also describes the doping of inherently conductive polymers with metal salts and recommends the use of AuCl.sub.3 as dopant.
Patent Applications WO-8 700 677 and EP-540 448 describe the doping of conductive polymers with FeCl.sub.3 or else compounds containing the FeCl.sub.4 anion.
As indicated above, the introduction of metal atoms into the conductive polymer or copolymer by the oxidizing compounds used for the doping of these conductive polymers or copolymers renders the resulting conductive polymers or copolymers incompatible with their use as photosensitive resins in lithography. In addition, apart from the polythiophene doped with AuCl.sub.3, the conductive polymers obtained are of low stability, especially under the effect of temperature and humidity.